Abstract: Fission yields are determined for the fission of 235 U induced by thermal neutrons by HPGe γ ray spectrometry. Absolute fission rate is monitored with a double fission chamber. The efficiency of the fission chamber is checked with absolute determination of 198 Au activity from 197 Au (n,γ) 198 Au reaction for the first time. Fission product activities of irradiated 235 U foils are measured by HPGe γ ray spectrometry without chemical separation.